1. Field of the Invention
The invention relates to an intermingled unsized synthetic filament yarn, in particular a synthetic filament yarn for manufacturing woven fabrics for air bags or other industrial applications, with a yarn titer of from 100 to 1000 dtex.
2. Description of the Related Art
Woven fabrics for manufacturing air bags must fulfill a number of very different requirements. In addition to the especially important specifically adjusted air permeability, these fabrics must have good aging resistance, high strength, good foldability, and a high degree of flexibility when the air bag is triggered as the result of a collision. Corresponding to the particular demands placed on the properties of the fabric, there are also very specific requirements for the yarns to be used. These requirements relate on the one hand to their effect on the properties of the fabric and on the other hand to their workability during fabric manufacture.
In practice, it has been difficult to meet all requirements in the manner desired by automobile manufacturers in particular.
The first air bags were made preferably from coated woven fabrics. These have not proven particularly satisfactory, not only because of their manufacturing costs but also due to several disadvantages during use.
After the increased appearance of uncoated air bag woven fabrics, the yarns initially employed had for the most part relatively high yarn and filament titers. While in most cases this permitted attainment of the required air permeability and strength, these fabrics were frequently unsatisfactory with respect to foldability and flexibility.
For woven fabric manufacture, the yarns cited were almost always sized when used for the warp, less frequently twisted. The weft often comprised unsized and untwisted yarns, although twisted yarns were also employed in the weft.
Both twisting and sizing considerably increase the manufacturing costs for the yarns and thus for the woven fabrics. In addition, the size must be removed after fabric manufacture, i.e., the fabric must be desized. This process poses problems from economical and ecological standpoints, since not only are costs involved for the desizing but additional costs are also incurred for the processing of the desizing baths that is mandated by ecological considerations.
Although the desizing costs do not apply in twisting, which involves roughly the same level of costs as sizing, there is another disadvantage in this case, since experience has shown that twisted yarns produce fabric with a more "granular" surface than untwisted yarns. Furthermore, when using twisted yarns, it is more difficult to establish a specific value of air permeability.
An improvement in foldability and flexibility can be attained if yarns are used with a relatively low titer for the individual filaments. Such yarns have already been proposed for making air bags.
In EP-A 442 373, a polyester filament yarn with a yarn titer of 250-550 dtex and a filament titer &lt;4 dtex is described for making uncoated air bag woven fabrics. The yarns, at least in the warp, are to have a twist of 110-130 T/m. The aforementioned disadvantage of using twisted yarns applies in this case.
In JP-A 04-209 846, the use of filament yarns with a yarn titer of 210-750 den (235-840 dtex) and a filament titer &lt;5 den (5.5 dtex) is recommended for air bag woven fabrics. The yarns can be untwisted, but a twisted yarn for the warp with a twist of &lt;200 T/m is proposed. In using twisted yarns, the aforementioned disadvantages arise; if untwisted yarn is employed in the warp, it would be nearly impossible to process it satisfactorily on the loom at a high fabric density without size.
The use of extremely fine individual filaments with a titer &lt;2 den (2.2 dtex) is described in JP-A 05-093 340 for air bag filter fabrics. In this case, it cannot be determined whether these yarns are to be unsized, something which would be nearly impossible in practice.
Polyamide yarns with filament titers of 1-6 den (1.1-6.7 dtex) and yarn titers of 70-840 den (80-940 dtex) are proposed in JP-A 06-041 844. It is not stated whether the yarns used are to be sized or unsized.
As is known in the weaving industry, processing of fine-filament yarns, especially warp yarns, is considerably more difficult than weaving coarse-filament yarns, since with fine-filament yarns there is a significantly greater risk of filament breaks and thus of so-called fluffs, which lead to stoppage of the loom as well as flaws in the fabric. For this reason, it has up to now been important to provide fine-filament yarns with a sufficiently large amount of size in order to ensure problem-free processing on the loom.
In the chemical fiber processing art, it is known that intermingling of the individual filaments can serve as an alternative to sizing.
The processing of intermingled yarns into woven fabrics for air bags is known. It is described in CA-A 974 745. As is demonstrated by the embodiment example of this document, the recommendation to use intermingled yarns applies to yarns with a high filament titer (6.7 dtex). Moreover, no statements are made concerning the degree of intermingling the yarns are to exhibit and what stability the intermingling points must have.
In JP-A 06-306 728, an air bag woven fabric is described that is made from intermingled multifilament yarns with a filament titer less than 3.3 dtex. The degree of intermingling of the yarns is to be at least 20 per m, i.e., the mean opening length is less than 5 cm. This document provides no teaching concerning what stability the intermingling points must have in order to ensure problem-free processing in the weaving mill.
Also, the use of intermingled yarns has often been described for making woven fabrics in the clothing industry. An example is DE-A 4 327 371, in which especially the processing of intermingled yarns with low opening tendency of the intermingling points of the yarns, with appropriate tension on the loom, is described.
Consequently, the prior art does not teach what steps must be taken to provide fine-filament yarns that can be processed satisfactorily without size into industrial woven fabrics, particularly air bag fabrics.